Dewaxing mineral oils



Jan. 9, 1934. R. N. 'GILES 1,943,235!

DEWAXING MINERAL OILS Filed Aug. s1', 19:51

. Patented Janv. 9, 1934 mais' 1,943,236 DEWAXING MINERAL oms Roy N. Giles, Casper; Wyo., assigner to Standard OilCompany, Chicago, lll.; a corporation of Indiana Application August 31, 1931. Serial No. 560,361

21 Claims.

This invention relates to the separation of wax from mineral oils and it pertains more particularly to a means for dewaxing lubricating oils so that they will have low pour points, or in other words, so that they will ow freely at'low temperatures.

In the dewaxing process it is common practice to dilute the wax-bearing oil with filter naphtha, chill the mixture to low temperatures for throwing the wax out of solution, and separate the wax from the diluted oil by filtering, settling or centrifuging. Some waxes, usually those of the .so-called paraflin distillate range, contain relatively low melting point waxes which on cooling form well dened crystals that may be vfiltered or sweated for the removal of oil therefrom. Other waxes, called ceresins, are usually present in heavy motor base stock; the ceresins are usually of relatively high melting point, and they separate out from iilter naphtha in a occulent form so that filtration and/or sweating is impossible. Between the paraflin distillate and the motor base stock there are slop Wax cuts whichcontain mixtures of paraiins and ceresins, and it has been practically impossible to separate these slop waxes from the oil because the amorphous structure prevents filtration, and because the crystalline structure and specific gravity may prevent eiective sedimentation or settling. An

, object of my invention is to provide an improved process for separating waxes of this type from oil.

A futher object is to provide an improved diluent for dewaxing processes. A further object is to provide a process for crystallizing the wax in such a manner that the crystals may be effectively filtered or settled without the use of settling agents or lter aids. A further objectl is to provide a nished oil of better color because of the lower reducing temperature made possible by the use of my improved diluent. A further object is to increase chilling rates and filter rates in a dewaxing process. A further object is to provide a cheaper, simpler and more effective dewaxlng process as hereinafter described.

I have discovered that liquefied butane has remarkable new andV unexpected properties as a wax diluent. Ceresins may be crystallized from liquid butane in a form which will permit rapid and emcient filtration. Mixtures of paraiiins and ceresins may likewise be crystallized so that they may be either filtered or settled.- A feature of the use of liquid butane is the complete solution of the waxbefore the chilling is begun, and to accomplish this solution I heat thewaxy oil with liquid butane at a temperature of about overhead lubricants of this (Cl. 196-18) I 140 F. and at a pressure of about 110 lbs. per sq. in. The refrigeration may be accomplished by conventional means or it may be very rapidly brought about by the vaporization of a portion-of the butane. I have discovered that the mixture may be chilled from 35 to 350 F. per hour and that the crystals formed by this rapid chilling can be readily filtered even though the wax mixtnure contains large amounts of ceresin wax.

My invention will be'more clearly understood 65 from the following description and from theaccompanying drawing wherein I have diagrammatically illustrated a dewaxing plant in accord- 1 ance with my invention.

The oil to be dewaxed may be a heavy petroleum distillate or steam refined residue, it being understood, of course, that different amounts of diluent will be used for oils of various compositions, viscosities,A etc. In my preferred example I will describe the dewaxing of a heavy lubricating oil which is commonly known as a motor base stock. This oil may be produced from Mid Continentv or any other crude petroleum, and it preferably has a flash point of about 470 F. and a viscosity at 210 F. of about 70-75 seconds Say- 80 bolt. The motor base stock may be a residualtreated steam refined oil or it may be an overhead lubricating stock; the invention is particularly applicable to thev latter case because type cannot be readily dewaxed by other methods.

In practicing my invention I utilize a closed system, parts of which are adapted towithstand pressures upwards of 150 lbs. This is necessary because I use a diluent which is gaseous at normal temperatures and pressures, and particularly at the temperatures to which it must be heated for effecting complete solution. As a diluent I use liquid butane, which may be pure butane or which may be a mixture of butane with isobutane 05 and/or small amounts of propane, pentane, etc. This mixture is usually defined by its vapor pressure, which in this case is about 20-50 lbs./ sq. in. at 70 F. and 50-150 iba/sq. in. att-130 F. Preferably its vapor pressure is 33 lbs. per sq. in. 100 at 70F. and 110 lbs. per sq. in. atl30 F.

Liquid butane from pressure storage tank 10 is discharged through pipe 11 and regulating valve 12 into heater 13 and thence through pipe 14 into mixer 15. Wax-bearing oil is introduced into the system by pipe 16 in amounts regulated by valve 17; it may be introduced directly into the mixer or it may be introduced into the butane line 14.

It is important that the wax be completely dissolved in the liquid butane before the chilling is initiated, and I have found that the mixture must be heated to a temperature of about 140 to 145 F. for efecting complete solution. If this step is omitted the crystal structure of the precipitated Wax may be of entirely unsatisfactory nature; it may be impossible to filter the same, and if lterable, the filtrate may be cloudy and the filter cake may contain a large amount of oil.

After the mixture of butane and waxy oil has been heated and mixed to eiect solution, the mixture is conducted by pipe 18 to cooler 19 which may be a heat exchanger or any other conventional apparatus for reducing the mixture to normal tem eratures. From cooler 19 the mixture is conveyed through pipe 20 and reducing valve 21 to rerigereting or chilling chamber 22.

The rerigeration may be accomplished. in any conventional manner; for instance, brine may be cooled in refrigerating plant 23 and circulated to from the chilling chamber by pipes 24. .I may, however, effect refrigeration by vaporizing a part of the butane and withdrawing butane vapors through pipe 25. rThe butane lighthydrocarbon mixtiue to be evaporated for effecting refrigeration may be introduced directly into the reirigerating chamber 22 by means of pipe 20A.

-ieretofore it has been deemed necessary to 'refrigerate or chill the oil-wax mixture at a slow even rate for obtaining desirable was: crystal structure. l. have discovered that when butane is used as a diluent the cooling rate may be increased from 35 to 350 F. per hour and that this high cooling rate produces crystals which can be readily filtered.

The mixture of diluted oil and wax crystals is removed from the bottom of refrigerating or chilling chamber 22, through pipe 26 and valve 27 and it is then introduced into wax filter 28. This lter may be of any desirable type and, per

. se, it forms no part of my present invention, so

that detailed description is unnecessary. i-lown ever, a closed type pressure lter is desirable. The wax from the lter is removed by pipe 29 to suitable apparatus for re-melting it and recovering the butano.

The diluted oil is discharged from the lter through pipe 30 into a sump 31 from which it is conveyed by pipe 32, pump 33 and pipe 34 to exchanger 35. In exchanger I may heat the mixture to a suiiiciently high temperature to effect practically complete vaporization of the diluent at the pressure of the storage tank which may be about 150 lbs. per sq. in. I may use a lower storage pressure, however, and force the butane into mixer 15 by means of a suitable pump (not shown),- and in this case the mixture may be heated to a somewhat lower temperature. The temperature will be somewhat dependent on the proportion of diluent present, but it will be in the range of about 350 to 450 F.

From exchanger 35 the gases and vapors are introduced by pipe 36 into ash drum 37, the butane vapors being discharged at the top of the drum through pipe 38, liquefied in condenser 39 and returned by pipe 40 to the butane storage tank 10.

Hot oil from flash drum 37 is drawn from the base thereof through pipe 41 and reducing valve 42. It is then flashed in low pressure ash drum 43. The heat contained in the liquid is usually sufficient to drive oi the last traces of diluent, and to leave the oil with a suiciently high flash point, but if desired additional heat may be introduced by means of coil 44. The nished oil is with- -drawn through pipe 45, and the butane vapors are withdrawn through pipe 46, compressed by pump 47, and forced through pipe 48 to condenser 49, wherein they are liquefied, the liquid butane being introduced into storage tank 10.

As hereinabove stated, the refrigeration step may be accomplished by the vaporization of a portion of the diluent, in which case, enough extra diluent should be added so that after refrigeration the proportion will be about '70 to 80 parts of diluent to 20 or 30 parts of oil. Filtration has been effected with as. high as 40% oil, but I found it more desirable to use the proportions above stated. The amount of butano or hydrocarbon mixture necessary for effecting refrigeration may be calculated for any given instance. and it may depend somewhat on the degree of insulation of the equipment. Roughly speaking, I use about one-hallc lb. of butane to lower the temperature o lbs. of liquid l F.

The butano vapors from refrigerator chamber 22 are withdrawn through pipe 25 and valve 5l .by means ci pump 47, and condensed and returned to storage together with butane vapors from low pressure flash drum 43. It should be understood,

however, that any other suitable means may be l00 employed for handling the refrigerant liquids and vapors.

I want to emphasize the importance of liquid butano on the crystal structure of the wax which is precipitated therein. that ceiesin wax was amorphous, but in butano it not only shows a crystalline structure, but it shows crystals which are readily lterable, which is an innovation in this art.

It has been assumed I have found that the wax may be separated from the oil by cold settling instead of by filtering. A even though substantial amounts of paraffin wax are present. This is apparently due to the extremely low specific gravity and low viscosity of liquid butane. 120, preferably about 114, and it weighs only 4.6 to 4.9, preferably 4.8 lbs. per gallon. The relative effectiveness of butane and filter naphtha as a settling agent is shown inthe following table,

Its A. P. I. gravity is from 108 to 115 wherein the last column is the difference in the density between the wax and solution divided by absolute viscosity.

Filter naphth diluent 125 Sp m Saybolt Absolute Relativo Diluent ratio 10 /o 'F vis. at viscosity settling.

10 F. at 10 F tendency 257 oil l .gg dillueutj 1 8250 45. l 0110 l. b4 130 oi 83g; dlluent 8121 31.0 .0402 I 3. 32 l oi 90,73 dilueut 1 .80a 35. 5 .0337 4.18

Butanc diluent 25 oil v ig? dlluent i001 31.5 .0170 13.96 oi gg'; dnllucut (i6/0 29. 8 .0082 3. 6l

0l 90%@ duent} .l .650 29.1 .0034 87.10 140 The effect of butane in decreasing the settling time will be apparent from the following table:

*('lhs solution showed no tendency to settle within a reasonable time so some of the oil was ltered.)

The primary object of the dewaxing operation is to produce a motor oil having a low cold test.

The cold tests produced by solutions 1 and 2 in mation, together with the characteristic properties (particularly low viscosity) of the diluent, combine to produce the desired result. In many instances I found that unless the waxy oil is heated with the liquid butane to effect complete solution the desired crystallization does not take place, and in that case the wax cannot be readily filtered or settled; I

I have found that chilling rates may beobtained of an entirely diierent order from those heretofore employed in the refrigeration of oilwax mixtures. Instead of limiting refrigeration to 4 or 5 per hour, I speed it up to from 35 to 350 per hour, preferably 150 F. per hour, and even at this high rate I have found that crystals are produced which may be readily filtered from or settled in the butane diluent.

While I have described in detail a preferred embodiment of my invention, it is understood that I do not limit myself to the details herein set forth', except as defined by the following claims, which should be construed as broadly as the prior art will permit. The term butane in these claims refers to a liquefied hydrocarbon having approximately the vapor pressure of normal butane, and therefore this expression shall include mixtures of butane with isobutane, pentane, propane, etc.

I claim:

i. The method of removing wax from a waxbearing oil which comprises heating said waxbearing oil with butane to eiect complete solution of oil and wax therein, reirigerating'the solution to cause crystallization of the wax, and mechanically separating said wax from said butane-oil mixture.

2. The combination of claim 1 wherein the temperature of heating is about 140 F., the butane being maintained under pressure to keep it in the liquid state.

3. The combination of claim 1 wherein the refrigeration is effected by the evaporation of a part of the diluent.

4. The method of obtaining fllterable wax cryslbearing oil, which comprises mixing said oil with tals which comprises dissolving wax in liquid butane and chilling the solution.

5. The combination of claim 4 wherein the rate of chilling is from 35 to 350 F. per hour.

6. The method of removing paraffin-ceresin wax mixtures from oil .which comprises dissolving said wax mixture in liquid butane, and rapidly chilling the mixture to about -20 F.

7. 'I'he method of removing wax from oil which comprises mixing about 3 or 4 parts of butane in the liquefied state with one part of a waxy oil at a temperature high enough to eect solution of the wax in the butane, coolingsaid mixture to about 20 F. to effect crystallization of the Wax, and mechanically separating the wax crystals from the butane-oil mixture.

8. The method of dewaxing petroleum oils which comprises mixing liquid butane with waxy oil at a temperature of about 140 F. to effect complete solution of the wax in the butane, cooling the mixture and refrigerating it to a temperature of about 20 F. to effect crystallization of the wax, mechanically separating the wax crystals from the butane-oil mixture,'removing the butane from the oil, and returning the butane to the system.

9. The method of dewaxing petroleum oils which comprises dissolving said oils in enough liquid butane to effect refrigeration by direct evaporation, and to leave about 7 parts of butane to 3 parts of oil and wax, chilling the mixture to about 20 F. by withdrawing butane vapors therefrom, compressing said butane vapors, liquefying them and returning them to the system, separating the Wax from the oil-butane mixture, separating the butane from the oil, and returning said butane to the system.

10. The method of removing wax from a waxbearing oilv which comprises heating said waxbearing oil with a normally gaseous hydrocarbon to an elevated temperature suflcient to effect complete solution of both oil and wax therein, refrigerating the solution to cause crystallization of the wax from the diluted oil in filterable form, mechanically separating said Wax frm said diluted oil, and separating the remaining diluent from the diluted oil.

1l. 'I'he method of removing wax'from a waxa normally gaseous. diluent, chilling the mixture by vaporizing at least a portion of the diluent and eiecting the chilling at a rate oisabout 150 F. per hour to cause crystallization of wax, and mechanically separating diluted oil from wax which is crystallized by the rapid chilling step.

12. The ymethod of separating wax from oil which comprises mixing said oil with a normally gaseous hydrocarbon diluent, vaporizing at least 'a part of said diluent to effect refrigeration at a rate of about 35 to 350 F. per hour and to a tem- 135 perature to cause the crystallization of wax in a readily iilterable form, and mechanically separating the crystallized wax from the diluted oil.

i3; In a process of dewaxing hydrocarbon lubricating oils the steps which comprise adding suiiicient liquid butane to said oil under pressure to both reduce its viscosity to permit ready separation of wax at dewaxing temperatures, and to provide the necessary refrigeration to bring the mixture to such temperature, reducing the pressure on said mixture to reduce the temperature by evaporation of butane to precipitate the wax, mechanically removing the wax, and recovering butane from the dewaxed oil.y

14. The process of separating hydrocarbon lubricatng oil and wax occurring naturally therewith which comprises heating said oil-Wax mixture with a normally gaseous, hydrocarbon refrigerant to an elevated temperature sufficient to effect complete solution of both wax and oil, effecting the major portion of the refrigeration necessary to precipitate the wax by evaporation of a portion of the hydrocarbon refrigerant thereby precipitating said wax, separating said precipitated wax, and recovering dewaxed lubricating oil from the remaining mixture.

15. The process of separating Wax from oil whichy comprises mixing with an oil-Wax mixture a liqueed normally gaseous hydrocarbon, maintaining the mixture at elevated temperature and at an elevated pressure suicient to effect complete solution of both wax and oil in the liqueed hydrocarbon, cooling the mixture to effect solidication of wax in separable form from the solution of oil in liquefied normally gaseous hydrocarbon, retaining at least a portion of the liqueed normally gaseous hydrocarbon in the oil to serve as a diluent therefor, and separating the solidified wax from the diluted oil.

16. The processof separating wax mixtures from heavy lubricating oil stock containing the. same which comprises 'dissolving one volume of said stock in at least two and one-half volumes of a liquefied normally gaseous hydrocarbon diluent at an elevated temperature and pressure, chilling the mixtureto devvaxing temperature at a rate of about to 350 per hour, mechanically removing the solidified wax from the oil-diluent solution, and removing the diluent from the oil.

17. The process of claim 16 wherein liqueed normally gaseous hydrocarbon diluent is rst separated from the oil at superatmospheric pressure so that the removed vapors may be condensed Leeaaae without being compressed and wherein the oil from the superatmospheric separator is passed to a low pressure zone for the nal removal of diluent from the oil.

18. The process of claim 16 wherein at least a part of the refrigeration is effected by the direct vaporization of a portion of the liquefied normally gaseous hydrocarbon from the diluted oilwax mixture.

19. The process of claim l wherein at least a part of the cooling is effected by removing diluent vapors from the diluted oil-wax mixture to effect refrigeration by vaporization, and wherein the removed diluent vapors are liquefied, cooled, and re-introduced into the diluted oilwax mixture.

20. The'process of claim 16 -wherein liqueiied normally gaseous hydrocarbon diluent is introducedinto the diluted oil-wax slurry at a point near the bottom of a body of said slurry.

2l. The process of separating wax mixture from heavy lubricating oil stock containing the same which comprises dissolving one volume of said stock in from two and one-half to twelve volumes of a liquefied normally gaseous hydrocarbon diluent at a temperature of about 140 F. and a pressure of at least 110 pounds per square inch, releasing the pressure on the system whereby the diluent is allowed to vaporize, removing said vapors at a rate to eect chilling ata rate of from 35 to 350 per hour, leaving at least about two and one-half parts of diluent per part of oil in the cooled slurry for facilitating wax separation, mechanically removing solidied wax from the diluted oil, removing diluent from the diluted oil by heating it at superatmospheric pressure, and nally removing the last traces of diluent at a lower pressure.

ROY N. GILES.

DiSCLAHVl ER DEWAXING- MINERAL OILS. Patent Disclaimer iled March 25, 1939, by the assignee,

Hereby enters this disclaimer to claim 13 in said specification.

[Ojcz'al Gazette April 18, 1.939.] 

